Reply To: Serve Scaled Image after Woocomerce update

In the past, theme authors had to make updates to settings directly via update_option calls to change the settings in the DB. This resulted in store owners experiencing issues where they would change image settings in the admin area just to have it revert back to what the theme updates it to on each page load. With WooCommerce 3.3 theme authors can now declare image sizes via the add_theme_support function. Declaring image sizes this way will take priority over any other settings and also hide the image settings section in the admin area.

from

https://woocommerce.wordpress.com/2017/12/11/wc-3-3-image-size-improvements/